The present invention relates to a means for hydraulic load compensated time delay.
In downhole well operations, there is often a need for a means that is able to provide a predetermined time delay in connection with an actuation or initiation of a tool that is to perform some work in the well. Often, it is only possible to actuate such means using tensile and/or compressive forces, for example through wireline operations.
It is further desirable that the time delay is predictable, which can present a challenge when the forces applied to the time delay means, using a long wireline, for example, may be difficult to control. It would be advantageous to be able to minimize the factors that could affect the duration of the time delay obtained in each case, and thereby simplify the calculation of the holding times necessary to effect a particular tool function. By compensating the means that creates the time delay for variations in the forces that are applied to the device, it is possible to achieve as constant, and thereby predictable, time delay as possible.
An example of a mechanically operated tool that may be actuated using a time delay means is a jar. In the actuation of a jar, a means is frequently used that tensions a spring, for example. The spring is released when it has a certain pretension and/or when a predetermined time period has elapsed. A wireline may be used for tensioning the spring, but the time needed for tensioning the spring is difficult to control because the force that is transferred through the wireline may drop off due to friction, stretching, and the like. Moreover, the mechanism generating the force is poorly controllable and hence unsuitable for fine adjustments. Thus, there is a need for a device that control the tensioning of the spring in a jar, for example, so that the tensioning time is largely independent of the tensioning force and any pulls or yanks that may occur. Therefore, it is desired to provide a system that gives a small resistance when the applied force is weak and that gives a larger resistance when the applied force is strong, wherein the resistance profile should be as proportional as possible to the applied force and fast reacting in order to absorb any sudden vigorous pulls.
The present invention provides a means that meets the above-mentioned needs.